September 07, 2017

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A New Approach to Represent Multi-Consumer, Multi-Species Soil Biogeochemical Reactions for Earth System Models

A new kinetics formulation (SUPECA) scales mixed reaction networks.

The Science

Environmental biogeochemistry emerges from microbially mediated redox reactions in a complex web of consumers and substrates. The two dominant approaches to represent these reactions, Monod and synthesizing unit (SU), are unable to scale consistently across complex reaction networks and fail to include substrate limitations, respectively. The authors here extend these approaches (termed SUPECA) to general redox reaction networks to improve terrestrial ecosystem biogeochemical modeling. The authors also applied the SUPECA approach to analyze the soil moisture constraint on soil organic matter (SOM) decomposition and compared results to a benchmark dataset to show that their approach accurately represents this constraint across a wide range of soil moisture conditions. The SUPECA approach is being applied in Next-Generation Ecosystem Experiments (NGEE)–Arctic modeling analyses and in the U.S. Department of Energy’s (DOE) Energy Exascale Earth System Model (E3SM) Land Model (ELM).

The Impact

The authors demonstrate that (1) existing Monod and SU kinetics are scaling inconsistently, (2) the new SUPECA kinetics rectifies these problems, and (3) that SUPECA is well suited to trait-based modeling approaches. The authors also show that SUPECA kinetics enables mechanistic modeling of soil moisture effects on organic matter decomposition.

Summary

SOM decomposition occurs in an extremely complex network of reactions, substrates, and consumers. To address this problem in a manner amenable to land model representation (e.g., E3SM’s ELM), the authors extended the equilibrium chemistry approximation (ECA) approach to generic biogeochemical networks that include redox reactions (termed SUPECA, or SU plus ECA, kinetics). The authors demonstrated that SUPECA consistently scales from single Monod type and redox reactions to a reaction network, while the popular dual Monod kinetics and SU kinetics fail to do so. It is also demonstrated that SUPECA kinetics is superior to dual Monod kinetics in modeling substrate competition in the presence of substrate-mineral interactions. By applying SUPECA to SOM decomposition, the authors showed that soil aggregates have significant impacts and illustrate potential flaws in current ESM land model approaches. The authors are applying the SUPECA approach in NGEE-Arctic modeling analyses and in DOE’s ELM.

Principal Investigator

William Riley
Lawrence Berkeley National Laboratory
wjriley@lbl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

DE-AC02-05CH11231 as part of the Next-Generation Ecosystem Experiments (NGEE)–Arctic project and Accelerated Climate Modeling for Energy (ACME) project, sponsored by the Office of Biological and Environmental Research within the U.S. Department of Energy Office of Science.

References

Tang, J.-Y., and Riley, W.J. "SUPECA kinetics for scaling redox reactions in networks of mixed substrates and consumers and an example application to aerobic soil respiration". Geoscientific Model Development 10 3277–3295  (2017). https://doi.org/10.5194/gmd-10-3277-2017.